The present invention relates to a method and apparatus for isolating faults in an internal combustion engine equipped with a catalytic converter and more particularly to a method and apparatus for determining internal combustion engine faults through analysis of the exhaust to determine hydrocarbon content, carbon monoxide content, and oxygen content. Isolation of faults in a non-catalytic converter equipped internal combustion engine may be found in my copending application Ser. No. 933,248, filed on the same day, titled "Fuel Burning Efficiency Determination System."
Present internal combustion exhaust diagnostic procedures based upon carbon monoxide and hydrocarbon emissions are inadequate when used on catalytic converter equipped engines. The purpose and end result of the catalyst is to remove carbon monoxide and hydrocarbon from the exhaust, which essentially masks any problems which were previously identifiable through emission analysis. Furthermore, problems in the engine may distort the performance of the catalytic converter and indicate a faulty converter while it is operating properly. Prior art has developed systems to isolate engine and catalytic converter problems, but these systems require complicated test techniques which are both costly and time consuming. These test techniques require close contact with and visual inspection of both the engine and catalytic converter.